The present invention concerns a steam generator, in particular a generator for generating pure steam, which comprises a feed line for conducting feed water into the steam generator, an electrode system for heating the water, a steam outlet from the generator, a separating space in the lower part of the steam generator, and a droplet separator through which the steam that has been generated is disposed to flow from the separating space to the steam outlet.
In multi-stage distilling apparatus, steam is required for steam supply to the different columns or stages. Usually, boiler steam is used which is impure. Impure boiler steam is very appropriate for use in multi-stage distilling apparatus, because the requirement of the steam supply is to merely cause efficient heat exchange with the heat exchange tubes in the columns.
Extremely strict quality requirements are imposed on pure steam, which is used for steam sterilizing in the pharmaceutical industry. The pure steam must be absolutely free of pyrogenic impurities as well. It must be kept in mind that the drug packaging may be defective. In this case, if the pure steam used in steam sterilizing is not absolutely free of pyrogens, then the result is that such drug packaging becomes unfit for use.
A pure steam generator is, in actual fact, a distilling apparatus without a condenser, with the pure steam being, in actual fact, the same as uncondensed distillate used, for instance, in solutions for injection use.
In pure steam generators, the purity requirements have been met in a prior art design, by the feed water itself being free of pyrogens. In that case, the pure steam that is produced is naturally free of pyrogens. However, using such high quality feed water causes tremendous costs. Therefore, this prior art design is not the best possible solution, from an economical point of view.
Therefore, impure feed water is usually used in pure steam generators presently known. The feed water is conducted with the aid of a feed pump, and along a feed line, usually through a waste water heat exchanger and a heating steam heat exchanger, and by a feed water flow connector into a distribution space at the upper end of the pure steam generator. From this space, the feed water flows downwardly in heat exchange with a heat exchange tube system, while from the lower end of the pure steam generator, the steam is conducted through a centrifugal separator to the pure steam outlet. The condensate of the heating steam is conducted to the heating steam heat exchanger, and the waste water to the waste water heat exchanger, for preheating the feed water.
Presently, electrically-heated pure steam generators are also used. A resistance boiler is not applicable in connection with rapid load change conditions, which is the situation when serving autoclaves intended for steam sterilizing. At the initial phase of steam sterilizing, much steam is rapidly required for supply of the autoclave, while after a certain time, the steam requirements drop abruptly.
A resistance boiler design is slow, requiring in practice, usually 10 to 20 minutes before any steam is produced if the feed water is cold. When the steam consumption ceases, a resistance boiler continues to produce steam for several minutes, as a result of which the pressure increases. The resistance boilers are usually fitted with a safety valve which then blows, whereby the steam that is produced goes to waste.
In fact, there are only two extreme situations in functioning of a resistance boiler design. One situation is when the boiler operates at full power, while the other situation is when there is no power at all. A resistance boiler also introduces the risk that the feed water boils dry. Moreover, the useful life span of electrical resistances is shorter in resistance boilers when they are run under varying load conditions.
The resistance boiler design has been improved by a solution in which the electrodes of the electrode system intended for evaporating or vaporizing the feed water, are located on the bottom of the tank in the water space. The drawbacks of this type of design known in the art are its slow operation, and a foaming problem. On the other hand, there is as a rule no risk of boiling dry. It is also a fact that in using this previously-known type of electrode, there is no possibility of achieving stepless power control, because the current intensity in relation to the water level is not adjustable.